Liquid flow assays, either employing a flow through device or of the lateral flow type, are well known for detection of a variety of analytes in liquid samples including antigens such as hormones, e.g. human chorionic gonadotrophin (hCG) for pregnancy testing, antibodies such as antibodies to infectious agents and haptens such as drugs of abuse. Flow through devices have been described which provide for single label detection in different patterns depending upon whether a negative or positive sample is applied. Such devices are described for example in European Patent no. 0217403 of Abbott Laboratories. Most commonly, known lateral flow devices, however, provide a control zone for establishing correct use of the device which is distal from the analyte detection zone in the direction of liquid flow. By way of example reference may be made to European Patent no. 0291194 of Inverness Medical Switzerland GmbH and related European Patent nos. 0560410 and 0560411, and European Patent no. 0284232 of Becton Dickinson. Published European Patent Application no. 0833159 (Millipore) describes further such devices providing a capture zone presenting immobilised analyte or analyte analog for capture of analyte/antibody complexes, multiple readout zones for binding of biotinylated analyte also carrying detectable label and a control zone which binds a second labelled irrelevant analyte carrying a second distinguishable label. EP-B 0566695 of Quidel Corp. describes lateral flow devices also employing two detectably distinguishable labelled reagents in which a detection zone is provided including a distinct control portion for capture of labelled control reagent. Manufacture of all such assay devices requires separate careful application to the test strip or sheet of immobilised reagent to provide the control region.
U.S. Pat. No. 6,258,548 (Buck) teaches lateral flow assays which provide distinguishable visual signals in a single combined detection and control zone indicative of negative and positive assays. However, the assay concept described is solely applicable to large antigens having more than one epitope and for which a labelled portion can be provided which is distinguishable by antibody binding from the whole parent antigen. For example, the whole antigen may be hCG and the labelled antigen portion the alpha domain of hCG. In this case, anti-alpha hCG antibody is immobilised in the detection zone of the test strip or sheet.
Assays of the present invention utilise a combined detection and control zone but are applicable to all types of analyte including haptens. They can utilise either a sandwich assay or competitive assay format and may be applied to haptens and antigens, including antibodies. Furthermore, in one embodiment the detection/control zone employed is a universal detection zone. This means identical strips or sheets comprising porous material and containing the detection zone can be manufactured for use in multiple assays for different analytes. For use in lateral flow assays, such a test strip or sheet may be joined with different label release zones, which provide the required labelled reagents.